The invention relates to a method for obtaining a map representation from digitized road segments and digitized objects, at least one road segment and at least one three-dimensional object being loaded from a database. The invention also relates to a navigation device for obtaining and for displaying the map representation.
JP 62-93614 A discloses a navigation device in which images of a multiplicity of predetermined points are stored inside a database. The appropriate image is output if a driver approaches such a points.
For this purpose, the images, as a rule buildings, must be individually photographed, digitized and inserted into a database with road segments at the corresponding coordinates. The outlay for this is considerable.
It is an object of the invention to provide a method for obtaining a map representation and a navigation device suitable for outputting the map representation which can make use for the substantially positionally accurate representation of three-dimensional objects within a road map of data that has been obtained automatically by means of aerial photographs.
This object can be achieved by a method for obtaining a map representation from digitized road segments and digitized objects, comprising the steps of:
loading a road segment from a first database,
loading a three-dimensional object from a second database,
comparing the geographic coordinates of the road segment with the geographic coordinates of the object,
if the road segment and the plan view of the object overlap one another in an overlap region, then displacing the road segment and the object so far relative to one another in a displacement direction, or reducing the base surface of the object so far, that the overlap region vanishes, and
outputting the road segment and the object in a fashion displaced relative to one another.
The road segments and objects may originate from different databases. The geographic coordinates of the object can be obtained by means of aerial photographs. The geographic coordinates of the road segment and of the object can be transformed into a common coordinate system. A displacement of road segment and object can be omitted when an overlap region remains upon reduction of the area of the object by at least 30%. A displacement direction, in which the object is displaced relative to the road segment, can be determined perpendicular to a line of intersection that is formed by the intersection points of the road segment with edges of the plan view of the object. The road segment can be provided with boundary lines. A displacement direction of the object relative to the road segment can be determined perpendicular to a line of intersection that is formed by the intersection points between the plan view of the object and that boundary line which is closest to the centroid of the plan view of the object. The magnitude of the displacement can be formed by the distance in the displacement direction between the point of the plan view of the object that projects furthest over the boundary line, and the boundary line. A displacement can be undertaken in at least two displacement directions, and in that the magnitude of the displacement is reduced in every displacement direction to a value below 100%. The object can be centered between two neighboring road segments. The base surface of the object can be reduced when, after a displacement, the plan view of the object touches or overlaps another road segment or the plan view of another object. An overlap region can be caused to vanish by modifying the spatial arrangement of the object relative to the road segment by means of a relaxation method. The dimensions of mutually bordering edges can be respectively reduced iteratively with the aid of the same reduction factor until the overlap region vanishes. Displacements of the object and reductions can be undertaken repeatedly in an alternating fashion.
Furthermore, the object can be achieved by a navigation device comprising a display device and a processor that is connected to at least one storage medium, wherein the navigation device further comprises means
for loading at least one road segment from a first database,
for loading at least one object from a second database,
for comparing the geographic coordinates of the road segment with the geographic coordinates of the object,
for displacing the road segment and the object relative to one another or for reducing the base surface of the object, provided that an overlap region occurs between the road segment and the plan view of the object, and specifically to such an extent that the overlap region vanishes, and
for the mutually displaced output of the road segment and the object on the display device.
The navigation device may further comprise an interface for transmitting a selected map representation from the navigation device to a portable data processing unit.
Since the map representation is obtained from two separate databases, it is possible for the purpose of representing three-dimensional objects such as buildings or prominent natural points in a road network to use data of objects that have been detected automatically with their coordinates by means of aerial photographs from aircraft or satellites and stored in a database. On the other hand, in order to represent the roads running in a map view it is possible to use already existing digital road maps that comprise a network of road segments with associated nodes. This digital road network can be used for calculating a route from a starting point to a target point selected by a user.
The three-dimensional objects are regularly stored by means of describing geometric shapes, for example as plane polygons, curved surfaces or so-called NURBS surfaces. In addition, it is also possible to store the surface for the corresponding object in the form of a texture in a further database.
Since the roads and the three-dimensional graphic objects are detected in different ways and with errors in each case, it is also possible for road segments and the plan views of the objects to overlap one another. In order to avoid a representation in which, for example, a building is placed in the middle of a road, road segment and object are, if appropriate, displaced relative to one another and/or the base surface of the object is reduced.
It is possible in this way to dispense with individual detection of a three-dimensional object, and with individually embedding it in a digital road map.
The three-dimensional scene modeling obtained according to the invention from the separate databases is suitable both for direct output onto a monitor of a navigation device or of a computer and for storage in a single database which can then be accessed by a terminal (navigation device or computer).
The magnitude by which an object must be displaced relative to a road segment is determined by the distance between a road segment or its boundary line and that point of the plan view of the object which projects furthest over the road segment or the boundary line.
If a plurality of lines of intersection are present between the plan view of an object and one or more road segments, a displacement direction is determined for each line of intersection. The displacement is then executed iteratively by means of a relaxation method, that is to say in each displacement direction the magnitude of the displacement is respectively cyclically fixed to be smaller than the distance there between the boundary line of a road segment and the point projecting furthest over the boundary line. After execution of a first displacement, or after execution of a first reduction of the base surface, a check is made in each displacement direction as to whether there is still a need for a further displacement step that is then, if appropriate, executed in the same way. A slow glide into an optimum is achieved by the relaxation. Displacement and scaling operations are executed in an alternating fashion in this way with the aid of a changing factor.
If the surface of the object is too large to be able to find space within neighboring road segments, a further relaxation method is applied by undertaking directional scaling (reduction) of the surface of the object. Said surface is reduced in a similar way in different directions, preferably while maintaining the proportions of the base surface, in several steps, if appropriate.
A map representation thus obtained with a realistic scene, which is distinguished by the representation of three-dimensional objects, can also be transmitted to a portable data processing unit. Such mobile data processing devices are known, for example, under the names of personal digital assistant, handheld PC or notebook. Individual scenes selected by a user can be transmitted to the mobile device via a wired interface or wireless interface such as Bluetooth. Such a scene permits a user to orientate him/herself on the spot. The transmission of the data can be performed from a home PC or, upon leaving a vehicle, from a navigation device.